Process for the reduction of alkaline earth metals and the production of alloys of aluminium



Nov. 14, G; N KIRSEBOM i PROCESS FOR THE REDUCTION OF ALKALINE EARTHMETALS AND THE PRODUCTION OF ALLOYS OF ALUMINIUM Filed July 2, 1952 wwwmd5/e faam a5 /Z a6.

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Patented Nov. 14, 1933 UNITED STATES PATENT OFFICE Gustaf NewtonKirsebom, slo, Norway,V assignor to Calloy Limited, London, England, ajoint-stock company of England Application July 2, 1932, Serial No.620,574, and in Norway January 23, 1932 23 Claims.

This invention relates to a method or process for the production ofaluminium alloys by reducing a compound or compounds of the alkalineearth metals in a bath of molten aluminium; and

further relates to. thel treatment of the dross,

Which forms in theheatng chamber while carrying out said process, forthe recovery of the metal or metals therefrom.

The method or .process for the production of aluminium alloys, accordingto the present invention, is carried out by introducing into a bath ofmolten aluminium a compound or compounds of the alkaline earth metalswhile vin other than powder form-for example in pieces grains or l5`lumps having the size of 1 or 2 mm. up to 100 mm. or more-to reduce saidcompound or compounds and thereby alloy said alkaline earth metal orAmetals with the aluminium.

In carrying out the said process or method according to the presentinvention, it will be found that all the alkaline earth metal producedduring the process does not alloy with the `aluminium but on thecontrary a considerable amount of the alkaline earth metal is left inthe crucible ormelting pot, or other heating chamber containing theheated charge, in the form of infusible dross; such dross sometimes yrunning higher in the alkaline earth metal than the proportion in thealuminium alloy; and it is an object of the present invention to treatthis dross for recovery or utilization of the metal or metals therein. f

The present invention comprises certain other features and certainmodications all of which will be fully described and set forthhereinafter.

Any known or suitable type of heating chamber such as a pot furnace orcrucible (all of which will hereinafter be referred to as the heatingvchamber) may be used; and the temperature to be employed would bebetween the melting point of aluminium (viz. 650 C.) and the vaporizingpoint of aluminium (about 1600 C.), the working range in operation beingsay between 700 C. and 1500 C.

The temperature is selected according to the compound or compounds to bereduced and the metal or metals to be alloyed with the aluminium and theamount (percentage) of such metal or metals which it is desired to alloywith a given amount of aluminium.

I employ the compound or compounds of the alkaline earth metal in otherthan powder form (i. e. any size above 12-mesh to the inch may beemployed) namely I employ the said compound 55 or compounds in piecesgrains, or lumps', of a size minium of any given weight will becalculated or 'under great evolutions of heat.

or sizes ranging between 1 or 2 mm. up to 100 mm.

or more; and I prepare said-pieces'grains.or

lumps by crushing or grinding or in any other suitable way.

The amount or proportion of the compound or compounds in such piecesgrains or lumps (either in mixed sizes, or graded approximately or asnearly as desired to any particular size or sizes) to be added to acharge or bath of molten aluregulated according to the amount of suchcompound or compounds which will have to be re- I duced in order to (a)allow for the metal which will become dross during the process and (b)provide the required percentage of the alkaline earth metal or metalswhich it is desired to alloy with the aluminium.

Having determined the temperature to be employed and the percentage ofthe alkaline earth 7 metal or metals which it is desired to bepresent inalloy with the aluminium (in the aluminium alloy tobe produced) theamount of the compound or compounds, in pieces grains or lumps, is thencomputed and fed to the'bath of molten aluminium; for instance .if thealuminium alloy is to contain ten percent of an alkaline earth metal insuch alloy then such an amount of the compound is fed to the bath ofmolten aluminium as will produce about 20% of the reduced metal, half ofwhich latter (or thereabouts) will becomey dross in the heating chambersand the other half (or thereabouts) become alloyed with the aluminium tothis produce the required ten percent of the alkaline earth metal inalloy with the aluminium.

My process for producing alkaline earth metal alloys with aluminium willnow be further d escribed as follows In carrying out the process withcalcium oxide; the pieces grains or lumps of calcium oxide are placed ontop of a bath of molten aluminium at the required temperature whereuponthe pieces grains or lumps of calcium oxide will gradually sink into themolten aluminium and the calcium 'oxide Will be reduced by the aluminiumand result in the formation of a calcium-aluminium 'alloy and aluminiumoxide; the reaction being as follows:-

The above reaction is essentially different from that which takes placein a process Well known as the Goldschmidt Thermit process in whichmetal oxides are treated with aluminium powder Now I have found that theabove calcium oxide aluminium reaction does not take place if thecalcium oxide is placed on top of the heated bath of aluminium in afinely divided state i. e. in powder form. On the other hand I havefound that a very satisfactory result is obained by placing upon the topof the bath of molten aluminium calcium oxide in pieces grains or lumpsof the size or sizes above referred to. I have found that the grains orpieces of calcium oxide sink into the molten aluminium and then reacttherewith (in contradistinction to the powder which does not sink intothe aluminium) and I have succeeded in this way in obtaining analuminium alloy containing up to 10% Ca. l

In carrying out the present invention with calcium oxide for instancethe following procedure may be adopted:-

Aluminium metal is first melted in preferably a crucible furnace andthen heated till the temperature has reached about or between 1000-1200C. Ordinary burnt lime (as low in iron as possible) is then added to thetop of the bath of molten aluminium in pieces ranging ordinarily from afew millimeters diameter to a walnut size. As the operation proceeds,the pieces of lime gradually sink into the molten aluminium bath;

whereas if the pieces are too small, e. g. if lime powder be used samewill not sink down into the molten aluminium but will float on the topand even after hours contact little or no calcium would be found in themetal.

The accompanying drawing illustrates a flow sheet of a suitable plantfor carrying out the process according to my present invention withcalcium oxide; or with any other compound or compounds of the alkalineearth metals.

After several hours of contact the pieces grains or lumps of calciumoxide will have been dissipated and the alloy is discharged havingreached the desired percentage el g. around 10% Ca. About fifty percentof the metals is however left in the heating chamber in the form ofinfusible dross of aluminium calcium alloy and usually running evenhigher in calcium than the molten aluminium itself.

I have found that an economic way of treating this dross is by smeltingit down under a covering of common salt in aifurnace at about 1000 C.

I have found that the calcium-aluminium alloy dross will react directlywith the sodium chloride under the reactions:

Thus the aluminium is recovered from this dross as substantially puremetal free from calcium. The calcium in the dross reacts with the sodiumchloride under release of sodium. This sodium will at this temperaturepartly be used up in reducing some of the oxidized aluminium and partlybe oxidized directly to NazO.

A good deal of this NazO fumes off on top of the bath and may berecovered in a fume bag. Some of it may be traced in the secondary drossformed in the salt melt. This secondary' dross will consist largely ofsodium and calcium chlorides with insoluble particles of aluminiumoxide, lime, etc. It may-be treated wih a caustic soda solution for therecovery of the contained aluminium, and this caustic solution may beproduced by wetting the fume of sodium oxide obtained during the saltreaction.

According to a further feature of this invention,

, dross containing 44% Sr., which decomposed wa- I have found that if,instead of adding only calcium oxide I also' add magnesium oxide inpieces grain or lump formas aforesaid, I obtain both calcium andmagnesium in the metal. During the salt treatment of the dross themagnesium will however not react with the sodium chloride and it is thuspossible if required to remove the calcium from the dross of calciummagnesium aluminium by melting it together with salt.

Furthermore I have found that the secondary dross will contain nitrides(probably of calcium). These nitrides can be discerned as small yellowparticles scattered in the mass. On wetting some of the dross with Waterand heating the mass, large volume of ammonia will be given off and canbe collected. It is therefore possible to obtain nitrogen from the airby this process in the form of ammonia, which may be collected.

By subsiituting barium oxide for lime, I have obtained a metalcontaining ,15% Ba. and a metallic dross, which was found to decomposewater` and contain 21% metallic barium.

By substituting strontium oxide for lime, I obtained a metal containing22% Sr. and a metallic ter violenly.

Similarly a. beryllium-aluminium alloy can be obtained, e. g. containing0.2% Be.

Also in these cases the dross may be treated with salt recovering thealuminium in metallic form and barium chloride, or strontium chloride orberyllium chloride, and ammonia as by-products.

It is also possible to treat the dross by other fluxes, such as forexample cryallite. The dross may then be added to a cryallite moltenbath and the pure aluminium recovered, while the oxidized aluminiumdissolved in the bath may be recovered by electrolysis.

By adding calcined magnesite in the form of pieces, grains or lumps toIthe aluminium I have obtained a Mg-Al-alloy containing up to 1.5% Mg.

Also I have found that when calcium-aluminium alloy is treated withmolten Mg-chloride the Mg will enter the metal and the calcium forms achloride.

I have also found that when calcium-aluminium alloy dross is meltedtogether with salt in the presence of magnesium oxide (calcinedmagnesite) some magnesium will enter into the aluminium.

I have also found'that the presence of calcium 130 oxide besidemagnesium oxide favours the preferential entrance of magnesium intoaluminium; and I therefore propose to use dolomites or burnt dolomites,which will give a calcium-magnesium aluminium alloy which may then beconverted l into a Mg-Al-alloy by eliminating the Ca either with salt orMgCl2;

It is also possible to introduce the alkaline earth metal compound as acarbonate, which will ultimately form an oxide before it reacts with the146 aluminium; and also any other alkaline earth metals compound, whichis capable of being broken up and delivering the oxide at thetemperature of the aluminium bath, may be used.

What I claim is:-

1. A process for the manufacture of alkaline earth alloys of aluminiumwhich comprises the steps of heating in a molten bath of aluminium,below the surface thereofVan oxygen-containing compound, other than asulphate, of the alkaline 150 earth metal, whereby a molten alloy and aninfusible alloy dross containing alumina are formed, and thereafterseparating the molten portion from the infusible dross.

2. A process foi the manufacture of alkaline earth alloys of aluminiumwhich comprises the steps 'of heating, in a molten bath of aluminium, anoxygen-containing compound other than a sulphate of the alkaline earthmetal in solid pieces of sufiicient size to overcome the surface tensionof molten aluminium and thereby sink below the surface of the bath,whereby a molten alloy and an infusible alloy dross containing aluminaare formed, and thereafter separating the molten portion from theinfusible dross.

3. A process for the manufacture of alkaline earth alloys of aluminiumwhich comprises the steps of vheating in a molten bath of aluminiumbelow the surface thereof, an oxide or carbonate of the alkaline earthmetal whereby a. molten alloy and an infusiblef alloy dross containingalumina are formed, and thereafter separating the molten portion fromthe infusible dross.

4. A process for the manufacture of alkaline earth alloys of aluminiumwhich comprises the steps of heating in a molten bath of aluminium anoxide or carbonate of the alkaline earth metal, in solid pieces ofsumcient size to overcome the surface tensionof molten aluminium andtherebysink below the surface of the bath, whereby a molten alloy and aninfusible alloy dross containing alumina are formed, and thereaftervseparating the molten portion from the infusible dross. y

5. A process for the manufacture of alkaline earth alloys of aluminiumwhich comprises the steps of heating in a molten bath of aluminium,below the surface thereof, a silicate of the alkaline earth metal,whereby a molten alloy and an infusible alloy dross containing aluminaare formed, and thereafter separating the molten portion from theinfusible dross.

6. A process for the manufacture of alkaline earth alloys ofaluminiumwhich comprises the steps of heating in a molten bath ofaluminium a silicate of the alkaline earth metal, in solid piecesvofsumcient size to overcome the surface tension of molten aluminium,whereby a molten alloy and an infusible alloy'dross containing aluminaare formed, and thereafter separating the molten portion from Ytheinfusible dross.

7. A process for the manufacture of alkaline earth alloys of aluminiumwhich comprises the steps of heating in a molten lbath of aluminium,below the surface thereof, an oxygen-containing compound, other than asulphate, of the alkaline earth metal, whereby a molten alloy and aninfusible alloy dross containing alumina are formed, thereafterseparating the molten pory tion from the infusible dross, and thefurther step of recovering-valuable constituents from the infusibledross.

8. A process for themanufacture of alkaline earth alloys of aluminiumwhich comprises in combination the steps oi heating in a molten bath ofaluminium, below the surface thereof, an oxygen-containing compound,other than a sulphate, of the alkaline earth metal, whereby a moltenalloy and an infusible alloy dross containing alumina are formed,thereafter separating the molten portion from the infusible dross,

recovering aluminium from the infusible dross` bymelting the latter witha reagent capable of forming a, salt' with the alkaline earthconstituent of the alloy therein, whereby a metallic layer and asecondary dross are formed, and. separating the metallic layer.

9. A process for the manufacture of alkalin earthealloys of aluminiumwhich comprises in combination the steps. of heating in a molten bath ofaluminium, below the surfacev thereof, an oxide or carbonate of thealkaline earth metal whereby a molten alloy and an infusible valloydross containing alumina are formed, thereafter separating the moltenportion from the infusible dross, recovering aluminium from theYinfusible dross by melting the latter with a reagent capable of forminga salt with the alkaline earth constituent ofthe alloy therein, wherebya metallic layer and a secondary dross are formed, and separating themetallic layer.

l0. A process for the manufacture of alkaline earth alloys of aluminiumwhich comprises in combination the steps of heating in a molten bath ofaluminium, below the surface thereof, an oxide or carbonate of thealkaline earth metal, whereby a molten alloy and an infusible alloydross containing alumina are formed, thereafter separating the moltenportion from the infusible dross, recovering aluminium from theinfusible dross by melting the latter with an alkali-halide, whereby ametallic layer and a secondary dross are formed, and separating themetallic layer.

ll. A process for the manufacture of alkaline earth alloys of aluminiumwhich comprises Ain combination the steps of heating in a molten bath ofaluminium, below the surface thereof, an oxide or carbonate of thealkaline earth metal, whereby a molten alloy and an infusible alloydross containing aluminal are formed, thereafter 110 separating themolten portion from the infusible dross, recovering aluminium from theinfusible dross `by melting the latter with sodium chloride, whereby ametallic layer and a secondary dross are formed, and separating themetallic 115 layer.

, 12. A process for the manufacture of alkaline earth alloys ofaluminium which comprises in steps of heating in a molten bath ofaluminium, an oxygen-containing compound, other than a 120 sulphate, ofthe alkaline earth metal, in solid pieces of suicient size to overcomethe surface tension of molten aluminium and thereby sink below thesurface of the bath, whereby a molten alloy and an infusible alloy drosscontaining alumina are formed, thereafter separating the molten portionfrom the infusible dross, and the further step of recoveringvaluableconstituents from the infusible dross.

13.- A process for the manufacture of alkaline earth ,alloys ofaluminium which ncomprisesy in combination the steps of heating in amolten bath of aluminium an oxygen-containing compound, other than asulphate, of the alkaline earth metal, in solid pieces of sufficientsize to overcome the surface tension of molten aluminium and therebysink below the surface of the bath, whereby a molten alloy and aninfusible alloy dross containing alumina are formed, thereafterseparating the molten portion from the infusible dross, recoveringvaluminium from the infusible dross by melting the latter with a reagentcapable ies ' of forming a salt with the alkaline earth constituent ofthe alloy therein, whereby a metallic layer and a secondary dross areformed, and separating the metalliclayer.

14. A process for the manufacture of alkaline earth alloys of aluminiumwhich comprises in combination the steps of heatingin a molten ybath ofaluminium an oxide or carbonate of the alkaline earth metal, in solidpieces of sufficient size to overcome the surface tension of moltenaluminium and thereby sink below the surface of the bath, whereby amolten alloy and an infusible dross containing alumina are formed,thereafter separating the molten portion from the infusible dross,recovering aluminium from the infusible dross by melting the latter witha reagent capable of forming a salt with the alkaline earth constituentof theA alloy therein, whereby a metallic layer and a secondary drossare formed, and separating the metallic layer.

I15. A process for the manufacture of alkaline earth alloys of aluminiumwhich comprises in alkali-halide, whereby a metallic layer and asecondary dross are formed, and separating the metallic layer.

16. A process for the manufacture of alkaline earth alloys of aluminiumwhich comprises in combination the steps of heating in a molten bath ofaluminium an oxide or carbonate of the alkaline earth metal, in solidpieces of sufficient size to overcome the surface tension of moltenaluminium and thereby sink below the surface of the bath, whereby amolten alloy and an infusible alloy dross containing alumina are formed,thereafter separating the molten portion from the infusible dross,recovering aluminium from the infusible dross by melting the latter withsodium chloride, whereby a metallic layer and a secondary dross areformed, and separating the metallic layer.

17. A process forthe manufacture of alkaline earth alloys of aluminium iwhich comprises in combination the steps of heating in a molten bath ofaluminium an oxide or carbonate of the alkaline earth metal, in solidpieces of 1/2 to 100 m. m. size, whereby a molten alloy and an infusiblealloy drosscontaining alumina are formed, thereafter separating themolten portion from the infusible dross, recovering aluminium from theinfusible dross by melting the latter with sodium chloride, whereby ametallic layer and a secondi combination the steps of heating in amolten bath of aluminium, below the surface thereof an oxide orcarbonate of thealkaline earthvmetal, whereby a molten alloy and aninfusible alloy dross containing alumina are formed, thereafterseparating'the molten portion from the infusible dross, recoveringaluminium from the infusible dross by melting the latter with analkali-halide, whereby a metallic layer and a secondary dross l areformed, separating the metallic layer, and

recovering alumina and ammonia from the secondary dross by heating thelatter with water.

19. A process for the manufacture of alkaline earth alloys of aluminiumwhich comprises in combination the steps of heating in a molten bath ofaluminium an oxide or carbonate of the alkaline earth metal, in solidpieces of sufficient size to overcome the surface tension of moltenaluminium andl thereby sink below the surface of the bath, whereby amolten alloy and an infusible alloy dross containing alumina are formed,thereafter separating the molten portion from the infusible dross,recovering aluminium from the infusible dross by melting' the latterwith an alkali-halide, whereby a metallic layer and a secondary drossare formed, separating the metallic layer, and recovering alumina andammonia from the secondary dross by heating the latter with water.`

20. A process for the manufacture of a calciumaluminium alloy whichcomprises the stepsof heating in a molten bath of aluminium, below thesurface thereof, calcium oxide or carbonate, whereby a moltencalcium-aluminium alloy and an alloy dross containing alumina areformed, and thereafter separating the molten portion from the infusibledross.

v21. A process for the manufacture of a calcium-aluminium alloy whichcomprises the steps of heating in a molten bath of aluminium calciumoxide or carbonate, in solid pieces of suiiicient size to overcome thesurface tension of molten aluminium and thereby sink below the surfaceof the bath, whereby a molten alloy and an infusible alloy drosscontaining alumina are formed, and thereafter separating the moltenportion from the infusible dross.

22. A process for the manufacture of calciumaluminium alloy whichcomprises in combination the steps of heating in a molten bath ofaluminium calcium oxide or carbonate, in solid pieces of sufficient sizeto overcome the surface tension of molten aluminium and thereby sinkbelow thesurface of the bath, whereby a molten alloy and an infusiblealloy dross containing alumina are formed, thereafter separating themolten portion from the infusible dross, recovering aluminium from theinfusible dross by melting the latter with sodium chloride, whereby ametallic layer and a secondary dross are formed, separating the metalliclayer, and recovering alumina and ammonia from the secondary dross byheating the latter with water.

23. A process forthe manufacture of a magnesium-aluminium alloy whichcomprises in combination the steps of heating in a molten bath ofaluminium calcium oxide or carbonate in solid pieces of suiiicient sizeto overcome the surface tension of molten aluminium and thereby sinkbelow the surface of the bath, whereby a molten alloy and an infusiblealloy dross containing alumina are oformed, thereafter separating themolten portion from the infusible dross, and treating the molten portionwith molten magnesium chloride.'

GUSTAF NEWTON KIRSEBOM.

